Periodic-combined-envelope-sequence generation device, periodic-combined-envelope-sequence generation method, periodic-combined-envelope-sequence generation program and recording medium

Abstract

An envelope sequence is provided that can improve approximation accuracy near peaks caused by the pitch period of an audio signal. A periodic-combined-envelope-sequence generation device according to the present invention takes, as an input audio signal, a time-domain audio digital signal in each frame, which is a predetermined time segment, and generates a periodic combined envelope sequence as an envelope sequence. The periodic-combined-envelope-sequence generation device according to the present invention comprises at least a spectral-envelope-sequence calculating part and a periodic-combined-envelope generating part. The spectral-envelope-sequence calculating part calculates a spectral envelope sequence of the input audio signal on the basis of time-domain linear prediction of the input audio signal. The periodic-combined-envelope generating part transforms an amplitude spectral envelope sequence to a periodic combined envelope sequence on the basis of a periodic component of the input audio signal in the frequency domain

What is claimed is: 
     
         1 : A periodic-combined-envelope-sequence generation device comprising:
 a spectral-envelope-sequence calculating part which takes, as an input audio signal, a time-domain audio digital signal in each frame which is a predetermined time segment, and calculates a spectral envelope sequence of the input audio signal on the basis of time-domain linear prediction of the input audio signal; and   a periodic-combined-envelope generating part which transforms the spectral envelope sequence to a periodic combined envelope sequence on the basis of a periodic component of the input audio signal in the frequency domain;   wherein the periodic-combined-envelope generating part modifies the periodic combined envelope sequence based on a value that determines a mixture ratio between the spectral envelope sequence and the periodic component.   
     
     
         2 : The periodic-combined-envelope-sequence generation device according to  claim 1 ,
 wherein the value that determines the mixture ratio is chosen such that the shape of the periodic combined envelope sequence and the shape of an absolute values of a coefficient string which is transformed from the input audio signal in the frequency domain becomes similar to one another.   
     
     
         3 : A periodic-combined-envelope-sequence generation method, executing:
 a spectral-envelope-sequence calculating step for taking, as an input audio signal, a time-domain audio digital signal in each frame which is a predetermined time segment, and calculating a spectral envelope sequence of the input audio signal on the basis of time-domain linear prediction of the input audio signal; and   a periodic-combined-envelope generating step of transforming the spectral envelope sequence to a periodic combined envelope sequence on the basis of a periodic component of the input audio signal in the frequency domain   wherein the periodic-combined-envelope generating step modifies the periodic combined envelope sequence based on a value that determines a mixture ratio between the spectral envelope sequence and the periodic component.   
     
     
         4 : The periodic-combined-envelope-sequence generation method according to  claim 3 ,
 wherein the value that determines the mixture ratio is chosen such that the shape of the periodic combined envelope sequence and the shape of an absolute values of a coefficient string which is transformed from the input audio signal in the frequency domain becomes similar to one another.   
     
     
         5 : A non-transitory computer-readable recording medium on which the periodic-combined-envelope-sequence generation program for causing a computer to function as the periodic-combined-envelope-sequence generation device according to  claim 1  is recorded. 
     
     
         6 : A non-transitory computer-readable recording medium on which the periodic-combined-envelope-sequence generation program for causing a computer to function as the periodic-combined-envelope-sequence generation device according to  claim 2  is recorded.